Driving assistance apparatus, driving assistance method, and non-transitory storage medium

The present application claims priority to Japanese Patent Applications number 2023-177554, filed on Oct. 13, 2023, contents of which are incorporated herein by reference in their entirety.

The present disclosure relates to a driving assistance apparatus, a driving assistance method, and a non-transitory storage medium for assisting a driving operation of a driver. A technique for avoiding a collision between a vehicle and a moving object is known. For example, Japanese Unexamined Patent Application Publication No. 2004-295620 discloses a technique of generating a maximum braking force achievable by a braking device of a vehicle that is reversing upon determining that a collision between the vehicle and a moving object (for example, another vehicle) is unavoidable on the basis of a relative position and a relative speed of the moving object with respect to the vehicle.

A distance between a reversing vehicle that is reversing and a moving object is sometimes detected to be shorter than the actual distance. In this case, it is sometimes determined that a collision between the reversing vehicle and the moving object cannot be avoided even though the collision between the reversing vehicle and the moving object actually is avoidable, resulting in a maximum braking force being generated.

The present disclosure focuses on this point, and an object thereof is to prevent a braking force from being excessive when avoiding a collision between a reversing vehicle and a moving object.

A first aspect of the present disclosure provides a driving assistance apparatus that includes a first acquisition part that acquires a first braking force enabling avoidance of a collision between a reversing vehicle that is reversing and a moving object approaching the reversing vehicle, a second acquisition part that acquires a second braking force on the basis of an amount of brake pedal depression, and a braking control part that causes the reversing vehicle to generate the first braking force if the first braking force is smaller than a maximum braking force of the reversing vehicle () and the second braking force is smaller than the first braking force.

A second aspect of the present disclosure provides a method for controlling a driving assistance apparatus, executed by a processor mounted on a reversing vehicle that is reversing, the method includes the steps of acquiring a first braking force enabling avoidance of a collision between the reversing vehicle and a moving object approaching the reversing vehicle, acquiring a second braking force on the basis of an amount of brake pedal depression, and causing the reversing vehicle to generate the first braking force if the first braking force is smaller than a maximum braking force of the reversing vehicle and the second braking force is smaller than the first braking force.

A third aspect of the present disclosure provides a non-transitory storage medium storing a program for causing a processor, mounted on a reversing vehicle that is reversing, to function as a first acquisition part that acquires a first braking force enabling avoidance of a collision between the reversing vehicle and a moving object approaching the reversing vehicle, a second acquisition part that acquires a second braking force on the basis of an amount of brake pedal depression, and a braking control part that causes the reversing vehicle to generate the first braking force if the first braking force is smaller than a maximum braking force of the reversing vehicle () and the second braking force is smaller than the first braking force.

Hereinafter, the present disclosure will be described through exemplary embodiments of the present disclosure, but the following exemplary embodiments do not limit the disclosure according to the claims, and not all of the combinations of features described in the exemplary embodiments are necessarily essential to the solution means of the disclosure.

[Configuration of Driving Assistance Apparatus]

A configuration of a driving assistance apparatusmounted on a reversing vehiclewill be described with reference to.illustrates an overview of the driving assistance apparatus.illustrates a configuration of the driving assistance apparatus.

A reversing vehicleis a vehicle that is reversing. The reversing vehicleis a truck, for example, but may be a passenger car. The reversing vehiclehas a detection device, a braking device, a speaker, and a driving assistance apparatusmounted thereon.

A moving objectis an object that is present around the reversing vehicleand is approaching the reversing vehicle. The moving objectis another vehicle (a motorcycle or a passenger car), a pedestrian, or a bicycle, for example, but is not limited thereto.

The detection devicedetects the moving objectaround the reversing vehicle. For example, the detection devicedetects a relative position, a relative distance, and a relative speed of the moving objectwith respect to the reversing vehicleby analyzing a captured image of an area behind the reversing vehiclein its direction of travel. The detection devicemay detect the relative position and the relative speed of the moving objectwith respect to the reversing vehicleby analyzing scanning data of Laser Imaging Detection and Ranging (LIDAR) that scans the area behind the reversing vehiclein its direction of travel, or may detect the relative position and the relative speed of the moving objectwith respect to the reversing vehicleusing other methods. Further, the detection devicemay detect the type of the moving objectby analyzing a captured image or scanning data. Specifically, the detection devicedetects whether the moving objectis a pedestrian or a light vehicle such as a bicycle, or whether the moving objectis a vehicle.

The detection deviceestimates an estimated pathof the moving object. For example, the detection deviceestimates the estimated pathof the moving objecton the basis of a relative position, a relative distance, and a relative speed of the moving objectwith respect to the detected reversing vehicle, but may estimate the estimated path using other methods.

The braking deviceis a device for decelerating the reversing vehicle. For example, the braking deviceis at least any of a drum brake or an auxiliary brake that generates a braking force. The drum brake achieves a braking force by pressing a brake shoe against a drum rotating together with a wheel of the reversing vehicle. The auxiliary brake is at least any of i) a retarder that achieves a braking force by directly applying a load to an output shaft of an engine of the reversing vehicleor ii) an exhaust brake that enhances an effect of engine braking by utilizing rotational resistance of the engine.

The speakeris a device that outputs sound. The speakeris controlled by the driving assistance apparatusto output sound. It should be noted that the speakermay be a buzzer that outputs a beeping sound or a transmission sound.

A depression amount acquisition deviceis a device that acquires an amount of brake pedal depression. The depression amount acquisition deviceinputs an amount of brake pedal depression to the driving assistance apparatus. The depression amount acquisition deviceis a sensor provided on a brake pedal, for example.

The driving assistance apparatusassists driving of a driver of the reversing vehicle. For example, the driving assistance apparatusassists in avoiding a collision between the reversing vehicleand the moving object. Specifically, if the moving objectapproaches an estimated paththrough which the reversing vehicleis estimated to pass, the driving assistance apparatusexecutes control for assisting with collision avoidance. The driving assistance apparatusestimates the estimated path. The estimated pathis an estimated path of the reversing vehicle. The driving assistance apparatusestimates the estimated pathon the basis of an angle and angular velocity of a steering wheel of the reversing vehicleand speed and acceleration of the reversing vehicle. It should be noted that a known technique can be used as a method for estimating the estimated path.

The driving assistance apparatusincludes a storageand a controller. The storageis a storage medium including a Read Only Memory (ROM), a Random Access Memory (RAM), a hard disk, and the like. The storagestores a program executed by the controller.

The controlleris a calculation resource including a processor such as a Central Processing Unit (CPU). The controllerimplements functions as a determination part, a first acquisition part, a second acquisition part, and a braking control partby executing the program stored in the storage.

The determination partdetermines whether or not the reversing vehicleand the moving objectare at risk of a collision. Specifically, the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision if the estimated pathof the reversing vehicleand the estimated pathof the moving objectintersect with each other. More specifically, the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision if the reversing vehicleand the moving objectarrive at an intersection position CP, where the estimated pathof the reversing vehicleand the estimated pathof the moving objectintersect with each other, at the same timing. The determination partdetermines that the reversing vehicleand the moving objectdo not collide with each other if the estimated pathof the reversing vehicleand the estimated pathof the moving objectdo not intersect with each other. In the following, a time at which the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision is referred to as a reference time.

If the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision, the determination partcauses the speakerto output a warning sound that notifies of an impending collision between the reversing vehicleand the moving object. Thus, the driver of the reversing vehiclerecognizes that there is a risk of collision between the reversing vehicleand the moving object. In the following description, it is assumed that the driver who recognizes that there is a risk of collision between the reversing vehicleand the moving objectdepresses the brake pedal.

If the reversing vehicleand the moving objectare determined to be at risk of a collision, the first acquisition partacquires a first braking force enabling avoidance of a collision between the reversing vehicleand the moving object. The first braking force is a braking force that results in stopping the reversing vehiclebefore the reversing vehicleand the moving objectcollide with each other. Specifically, the first braking force is a braking force that results in deceleration to stop the reversing vehiclebefore a time until collision between the reversing vehicleand the moving objectelapses. The time until collision is a time required for the reversing vehicleand the moving objectto reach the intersection position CP while maintaining the speed determined at the reference time.

The first braking force is represented by a function including a time as a variable and deceleration as a coefficient. The first braking force is represented by a linear function including i) an elapsed time from the reference time as a variable and ii) deceleration as a coefficient. For example, the deceleration is a ratio of the speed of the reversing vehicleat the reference time with respect to a value obtained by subtracting a predetermined time from the time until collision. The predetermined time is determined in consideration of safety and is 200 milliseconds, for example, but is not limited thereto. As a specific example, if the time until collision is 2000 milliseconds, the first acquisition partacquires a linear function, as a function representing the first braking force, using i) an elapsed time as a variable and ii) deceleration, obtained by dividing the speed of the reversing vehicleat the reference time by 1800 milliseconds, as a coefficient.

A second acquisition partacquires a second braking force corresponding to the amount of brake pedal depression inputted from the depression amount acquisition device. It is assumed that the relationship between the amount of depression and the second braking force is stored in the storage. Specifically, the storagestores a data table associating each of a plurality of amounts of depression having different magnitudes with the second braking force corresponding to each amount of depression. It should be noted that, in the present embodiment, it is assumed that the driver increases an amount of brake pedal depression with a constant force, and the second acquisition partacquires the second braking force that increases in accordance with the increased amount of brake pedal depression.

The braking control partcontrols the braking deviceto cause the reversing vehicleto generate the braking force. If the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision, the braking control partcauses the braking deviceto generate the first braking force or the second braking force. Details of an operation of the braking control partwill be described later.

illustrates the braking force that the reversing vehicleis caused to generate. In, the horizontal axis represents time t, and the vertical axis represents a braking force F. A reference time tis a time at which the determination partdetermines that the reversing vehicleand the moving objectare at risk of a collision. A dash-dotted line Frepresents a change over time of the first braking force. The first braking force increases over time at an increasing rate corresponding to the deceleration.

A dash-double-dot line Frepresents a change over time of the second braking force. The second braking force increases in accordance with the increased amount of brake pedal depression. As shown in, the second braking force is smaller than the first braking force, and an increasing rate of the second braking force is smaller than an increasing rate of the first braking force.

A broken line FM shows a change over time of a maximum braking force. The maximum braking force is the greatest braking force that the reversing vehiclecan generate. Specifically, the maximum braking force is a braking force that decelerates the reversing vehicleat the maximum deceleration that the reversing vehiclecan generate. A solid line Fa represents a change over time of the braking force that the braking control partactually causes the reversing vehicleto generate.

illustrates a change in the speed of the reversing vehicle. In, the horizontal axis represents the time t and the vertical axis represents speed V of the reversing vehicle. A time TC is a time at which the reversing vehicleand the moving objectare expected to collide with each other. In other words, the time TC is a time at which the time until collision has elapsed from the reference time t.

A dash-dotted line Vrepresents a change of the speed of the reversing vehicleif the vehicle is decelerated with the first braking force. If the braking devicedecelerates the reversing vehiclewith the first braking force, the reversing vehiclecan stop at a time TA, which is before the time TC, thereby avoiding the collision between the reversing vehicleand the moving object. A dash-double-dot line Vrepresents a change in the speed of the reversing vehicleif the vehicle is decelerated with the second braking force. If the braking devicedecelerates the reversing vehiclewith the second braking force, the reversing vehicleis expected to stop after the time TC, and thus the reversing vehicleand the moving objectmay collide with each other.

Therefore, if the second braking force is smaller than the first braking force and the reversing vehiclemay collide with the moving object, the braking control partcauses the reversing vehicleto generate the first braking force. Specifically, if the first braking force is smaller than the maximum braking force of the reversing vehicleand the second braking force is smaller than the first braking force, the braking control partincreases the braking force of the reversing vehicleuntil the braking force reaches the first braking force. More specifically, the braking control partcauses the reversing vehicleto continue generating the second braking force while the second braking force is smaller than the first braking force and a difference between the first braking force and the second braking force is less than a predetermined value D.

If the second braking force continues to be smaller than the first braking force and the difference between the first braking force and the second braking force becomes equal to or greater than the predetermined value D, the braking control partincreases the braking force of the reversing vehicleuntil the braking force reaches the first braking force. The braking control partsets the predetermined value D so that the braking force can be the first braking force by the time TC at which the collision is expected. In this way, the braking control partenables the driver to operate the reversing vehiclewithin a range in which a collision can be avoided.

As shown in, the braking control partcauses the reversing vehicleto generate the second braking force from the reference time tthe time t. The braking control partincreases the braking force at an increasing rate that is greater than the increasing rate of the second braking force from the time tat which the difference between the first braking force and the second braking force becomes equal to or greater than the predetermined value D. Then, at a time tthat is after the time t, the braking force generated by the braking control partbecomes the first braking force. The braking control partincreases the braking force from the time tusing a function representing the first braking force.

A solid line Va inrepresents a change in the speed V of the reversing vehiclewhen the reversing vehicledecelerates with the braking force the braking control partcauses the reversing vehicleto generate. The speed of the reversing vehicleis reduced at a second deceleration corresponding to the second braking force from the reference time tthe time t. Subsequently, the braking control partincreases the braking force until the braking force reaches the first braking force from the time tto the time t, thereby increasing the deceleration of the reversing vehicle. Thus, the reversing vehicledecelerates at a third deceleration which is larger than the second deceleration corresponding to the second braking force. Subsequently, after the time t, the braking control partcauses the reversing vehicleto generate the first braking force. Therefore, the speed of the reversing vehicleis reduced at a first deceleration corresponding to the first braking force. It should be noted that the first deceleration is smaller than the third deceleration. The reversing vehiclethen stops at the time TA, which is before the time TC, thereby avoiding the collision between the reversing vehicleand the moving object.

As described above, the braking control partcauses the reversing vehicleto generate the first braking force that is smaller than the maximum braking force, when avoiding the collision between the reversing vehicleand the moving object. As a result, the braking control partcan prevent the braking force of the reversing vehiclefrom becoming the maximum braking force which is an excessive braking force when avoiding the collision between the reversing vehicleand the moving object.

If the driver depresses the brake pedal sufficiently strongly, the second braking force becomes equal to or greater than the first braking force. In this case, the braking control partcauses the reversing vehicleto generate the second braking force. Specifically, while the second braking force continues to be equal to or greater than the first braking force, the braking control partcauses the reversing vehicleto continue generating the second braking force. Since the reversing vehiclestops before the time until collision elapses if the second braking force is equal to or greater than the first braking force, the collision between the reversing vehicleand the moving objectcan be avoided only by an operation of the driver.

By the way, there are cases where the second braking force is initially equal to or greater than the first braking force but becomes smaller than the first braking force. If the driver who strongly depresses the brake pedal is startled by activation of an anti-lock brake system (ABS) and eases off the pressure on the brake pedal, for example, the second braking force may decrease to be smaller than the first braking force. In this case, the collision between the reversing vehicleand the moving objectcannot be avoided.

Therefore, if the second braking force becomes smaller than the first braking force, the braking control partcauses the reversing vehicleto generate the maximum braking force. For example, if the second braking force becomes smaller than the first braking force after a predetermined time elapses from the reference time t, the braking control partcauses the reversing vehicleto generate the maximum braking force regardless of the difference between the first braking force and the second braking force. Specifically, if the second braking force becomes smaller than the first braking force after the predetermined time elapses from the reference time tin a state where the second braking force continues to be equal to or greater than the first braking force, the braking control partincreases the braking force that the reversing vehicleis caused to generate until the braking force reaches the maximum braking force. The predetermined time is a time obtained by subtracting a time required for the reversing vehicle, traveling at speed Vat the reference time t, to stop with the maximum braking force from the time until collision. As a specific example, if the time until collision is 2 seconds and the time required for stopping with the maximum braking force is 1 second, the predetermined time is 1 second. In this way, the braking control partcan avoid the collision between the reversing vehicleand the moving objecteven if the driver eases off the pressure on the brake pedal.

It should be noted that, if the first braking force at the reference time tis equal to or greater than the maximum braking force, the braking control partcauses the reversing vehicleto generate the maximum braking force regardless of the amount that the brake pedal is depressed by the driver. In this way, the braking control partcan reduce damage caused by the collision between the reversing vehicleand the moving objecteven if the collision between the reversing vehicleand the moving objectcannot be avoided.

The braking control partmay change the braking force that the reversing vehicleis caused to generate depending on the type of the moving object. For example, damage in a collision when the moving objectis a pedestrian tends to be greater than damage in a collision when the moving objectis a vehicle. Therefore, if the moving objectis any of a pedestrian or a light vehicle such as a bicycle, the braking control partgives priority to safety and causes the reversing vehicleto generate the maximum braking force. Specifically, if it is determined that there is a risk of collision between the reversing vehicleand the pedestrian, the braking control partcauses the reversing vehicleto generate the maximum braking force regardless of the first braking force, the second braking force, and the time until collision (see the broken line FM in). More specifically, the braking control partcauses the reversing vehicleto continue generating the maximum braking force until the reversing vehiclestops. In other words, the braking control partcauses the reversing vehicleto continue decelerating at the maximum deceleration that the reversing vehiclecan generate.

When decelerating at the maximum deceleration, the reversing vehiclestops at a time TM, which is before the time TA when stopping occurs with the first braking force (see the broken line VM in). As described above, the braking control partcauses the reversing vehicleto generate a greater braking force to stop the reversing vehiclesooner, thereby improving safety for pedestrians, bicycles, and the like.

If the moving objectis a vehicle, the braking control partcauses the reversing vehicleto generate the first braking force as described above. Accordingly, the braking control partcan prevent the braking force from being excessive when avoiding a collision between the reversing vehicleand the vehicle.

[Collision Avoidance Process]

is a flowchart illustrating an example of a collision avoidance process. The collision avoidance process is executed upon determining that there is a risk of collision between the reversing vehicleand the moving object.

First, the braking control partdetermines whether or not the moving objectis a pedestrian (step S). Specifically, the braking control partdetermines whether the moving objectis a pedestrian or a vehicle on the basis of a detection result of the detection device. If the moving objectis a pedestrian (Yes in step S), the braking control partcauses the reversing vehicleto generate the maximum braking force that the reversing vehiclecan generate (step S). Specifically, the braking control partcauses the reversing vehicleto continue generating the maximum braking force until the reversing vehiclestops. When the reversing vehiclestops, the braking control partends the collision avoidance process. The braking control partcauses the reversing vehicleto keep generating the maximum braking force even after ending the collision avoidance process.

If the moving objectis a vehicle (No in step S), the first acquisition partacquires the first braking force enabling avoidance of a collision between the reversing vehicleand the moving object(step S). Further, the second acquisition partacquires the second braking force corresponding to the current amount of brake pedal depression (step S). It should be noted that step Smay be performed before step S, or may be performed in parallel with step S.

The braking control partdetermines whether or not the second braking force is smaller than the first braking force (step S). If the second braking force is smaller than the first braking force (Yes in step S), the braking control partcauses the reversing vehicleto generate the first braking force (step S). Specifically, the braking control partincreases the braking force until the braking force reaches the first braking force. If the second braking force is equal to or greater than the first braking force (No in step S), the braking control partcauses the reversing vehicleto generate the second braking force (step S).

If the braking control partcauses the reversing vehicleto generate the first braking force or the second braking force, the braking control partdetermines whether or not the reversing vehiclehas stopped (step S). If the reversing vehiclehas not stopped (No in step S), the braking control partrepeatedly executes steps Sto Suntil the reversing vehiclestops. If the reversing vehiclehas stopped (Yes in step S), the braking control partends the collision avoidance process. Specifically, the braking control partends the collision avoidance process. The braking control partcauses the reversing vehicleto keep generating the first braking force or the second braking force even after ending the collision avoidance process.

[Effects of Driving Assistance Apparatus]